Each community is different and therefore requires different metrics for data-driven decisions about building and supporting it. The CHAOSS Project was started to help understand open source communities through metrics. We have had many conversations and realized that everyone cares about a different aspect of the community. This talk will share what we have learned in the CHAOSS Project about having metrics for open source communities. Once the right metrics have been decided on, challenges need to be overcome, both technical and organizational challenges. Finally, this talk will share real-world examples of how open source community metrics have been used to help build and support open source communities.